Textile material



' RELATIVE VISCOSITY p 24, 1963 J. M. CHRISTENS EIAL 3,104,450

I TEXTILE MATERIAL Filed Jan. 12, 1960 5o 29 I'll, I 25 27 PRIOR ART PILLING AREA n +0.5x B\ l6 *0.5x K /5{ F K 2 T1 l5 +0.5

0 Y I I4 0.5x 4 0 A i l3 +0.5:

2 FROSTING AREA I2 +0.5x I

0 5 l0 I5 5o 55 BREAK ELONGATION,

INVENTORS JOHN M. CHRISTENS ROBERT DANIEL GINTIS J. KIRKPATRICK ATTORNEY United States Patent 3,104,450 TEXTILE MATERIAL John M. Christens, Grifton, and Daniel Gintis, Kinston, N.C., and Robert J. Kirkpatrick, Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Jan. 12, 1960, Ser. No. 2,071 9 Claims. (Cl. 57-440) This invention relates to improved textile fibers from synthetic linear polyesters. More particularly, it relates to a new and improved drawn staple fiber comprised of polyethylene terephthalate.

The production of a novel class of fiber-forming linear polyesters of terephthalic acid and a glycol of the series HO(CH OH where n is an integer from 2 to 10, inelusive, has been fully disclosed by Whinfield and Dickson in US. Patent 2,465,319. The most important example of this class of polyesters is polyethylene terephthalate which has gained wide commercial acceptance in the form of both fiber and film. Fabrics prepared from fibers of polyethylene terephthalate have become well known for their ease-of-care properties associated with fast drying, crease recovery, and wrinkle resistance. They are also known for their strength and abrasion resistance. However, the entry of polyethylene terephthalate staple fiber into certain end uses has been greatly impeded by a phenomenon known as pilling which is a term used to refer to the formation of little balls on the surface of a fabric due to the entanglement of loose fiber ends, usually including pieces of lint which have been attached to the fabric surface. Many attempts have been made to eliminate this phenomenon of pilling by various fabric treatments, but these attempts have met with only limited success. Such fabric treatments include special combinations of brushing, shearing, and singeing to remove loose fiber ends from the fabric surface.

Many attempts have also been made to modify the polyethylene terephthalate fiber itself in order to inhibit the tendency to pilling in staple fabrics, e.g., by reducing the molecular weight of the polymer from which the fibers were spun. Such attempts have not proved to be successful, however, since new disadvantages and new problems were experienced with the low molecular weight fibers. For example, low molecular weight polyethylene terephthalate was found to be subject to fibrillation, the break-up of filaments into fibrils, which showed up in dyed fabrics as a frosting effect at points of greatest wear. The term frosting refers to the visual effect produced when an area of a dark-colored fabric becomes much lighter in color.

Various chemical treatments have been tried in order to inhibit pilling. However, these treatments have met with limited success. Further, it is obvious that a chemical treatment for fabrics is much less desirable than a method of building pill-resistance into the original fibers.

Therefore, it is an object of this invention to provide polyester staple fibers which have a high resistance to pilling and frosting when incorporated in a textile fabric. A further object is the provision of pill-resistant polyethylene terephthalate yarn and fabrics which are resistant to fibrillation and the accompanying fabric frosting effect. Other objects of this invention will be apparent from the detailed description which follows.

Unexpectedly, it has been found that by controlling the relative viscosity of the polymer and the tensile properties of the fiber within very narrow limits, drawn polyester and copolyester staple fiber can be prepared which, when woven into a fabric, exhibits a remarkably high resistance to pilling without suffering from an excessive increase in tendency towards fibrillation with its accompanying frosting effect. The critical limits for the relative viscosity of the polyethylene terephthalate polymers from which the fibers of this invention are prepared are in the range from 13.5 to 16.5 and preferably in the range from 14.5 to 15.5. The relative viscosity of fibers spun from copolymers of polyethylene terephthalate modified to include up to about 8% of additional ester linking units is similarly restricted with the exception that the viscosity limits must be increased by 0.5 unit for each mol percent of added copolymer component, as hereinafter defined. This well defined low viscosity range contrasts sharply with the higher relative viscosity range of 25 to 28 heretofore believed to be necessary in the preparation of polyethylene terephthalate fibers which were to be used in textile materials.

In addition to controlling the relative viscosity within the narrow limits specified, the fiber break elongation must be controlled. Break elongation within the range from about 26% to about 55% are acceptable; however, a particular relationship between the relative viscosity and the break elongation must be maintained in order to provide fibers which do not exhibit frosting when spun into yarns and woven into fabrics. The relationship between the relative viscosity and the break elongation is shown in the drawing.

Referring now to the drawing, in the graph the break elongation of the fibers is plotted as the ordinate and the relative viscosity of the polymer is plotted as the abscissa. The area ABC defines the critical parameters of the homopolyester fibers of this invention. As noted on the graph, in the region outside the area ABC and above a relative viscosity of 16.5, pilling occurs. In the region outside the area ABC and below a relative viscosity of 16.5, frosting occurs. As previously noted, the viscosity limits must be increased by 0.5 unit for each mol percent of added copolymer component. The letter at is used to represent the mol percent of the additional ester-linking units.

Referring again to the graph, the fibers of this invention must have a relative viscosity and a break elonga-. tion within the area represented by the area ABC. The preferred fibers which exhibit optimum balance of antipilling and anti-frosting are defined by the area DEF.

In general the fibers of this invention may be prepared by known methods. Polymerization may be carried out by known methods. The relative viscosity of the polytner may be controlled by a number of methods, e.g., by using a particular catalyst as described in U.S. Patent 2,650,213, by using a polymer chain'terminator as described in US. Patent 2,758,105, or by using special equipment as described in US. Patent 2,758,915.. The polymer is then spun into fibers which are cold drawn from about two to five times their original length. Various after-treatments, e.g., crimping, heat setting and relaxing, heat shrinking, dyeing, and other conventional treatments may be used withoutadversely affecting their high resistance to pilling and fibrillation.

In the specification and claims by the term relative viscosity it is meant the ratio of the viscosity of a 10% solution of polyethylene terephthalate in a mixture of 10 parts of phenol and 7 parts of 2,4,6-trichlorophenol (by weight) to the viscosity of the phenoltrichlorophenol mixture, per se, measured in the same units at 25 C.

By the term break elongation it is meant the percent extension which a fiber undergoes when stretched to the breaking point. More specifically, the term break elongation refers to the maximum extension of a one-inch fiber sample measured after boil-off using an Instron tensile tester.

The term polyethylene terephthalate used herein refers to the homopolyester of ethylene glycol and terephthalic acid. The term copolymers of polyethylene terephthalate as used herein refers to modified polyethylene terephthalates in which at least 92% of the recurring structural units are i.e., polyethylene terephthalate copolymers containing residues of other dicanboxylic acids or other glycols, in significant quantities. For example, in some preferred modifications the polyethylene terephthalate copolymer may contain recurring polyester linking units such as aliphatic acids, glycols, and hydroxy acids, e.g., those selected from the series HO(CH OH, Where x is an integer from 2 to 10, HOOO(CH ),,.COOH, where y is or an integer from 1 to 8, HO(CH COOI-I, Where z is an integer from 1 to 9, wherein the radicals (CI-1 (CI-1 and (CH may contain a radical of the type (C H O) where n is an integer from 2 to 4 and a is an integer from 1 to 300. Other polyester linking units may be selected from the series isophthalic acid, phthalic acid, naphthalic acids, and bibenzoic acids.

A commercially important example of the copolymers of polyethylene terephthalate is one which is modified to include sulfonate groups to increase its affinity for dyes as defined in the copending application of Griffing and Remington, U.S. Serial No. 622,811, filed November 19, 1956, and now US. Patent No. 3,018,272. The sulfonate modification is introduced by incorporating a copolymerizable compound containing at least one ester-forming functional group and at least one sulfonate group in the form of a metallic salt in the polyester, for example K, Na, Ca, Pb, and La salts, and the like. The copolymerizable compound becomes a repeating radical of the polymeric structure and is incorporated into the polymer chain through carboxylic ester linkages. As defined herein, the relative viscosity limits of this copolymer must be shifted to a higher viscosity by 0.5 unit for each moi percent of copolymer modification in order to maintain anti-piliing and anti-frosting properties. Although the pilling properties and frosting properties of the fibers of this invention are maintained up to the 8% limit of copolymer modification, it is usually undesirable to exceed about 3.5 mol percent of such modification since above this limit the Wash-and-wear properties tend to suffer. A preferred copolymer modification contains in the polymer chain about 2 mol percent of sodium 3,5-di(carboxy)benzenesulfonate. For the copolymer modification containing up to 3.5 mol percent of sodium 3,5-di(carboxy)benzenesulfonate, or the modification with any of the sulfonate groups disclosed in the aforementioned copending application of Grifling and Remington, the preferred relative viscosity can be readily determined by adding 0.5 unit for each moi percent of suifonate added to the polyethylene terephthalate. By referring to the accompanying drawing, the preferred range of relative viscosities for the 2% sulfonated isophthaiate copolymer modification is found to be from about 15.5 to 16.5.

The present invention therefore encompasses fiberforming material comprised of polymeric material taken from the class consistingof polyethylene terephthaiate in which the recurring structural unit is having a relative viscosity in the range from about 13.5

in the range associated with the present commercial staple fibers spun from polymers having relative viscosities of 25 to 28, Le, filament deniers in the range of 1.5 to 6.0, tenacities in the range 2.8 to 4.2 grams per denier, initial modulus in the range 30 to 60 grams per denier,

and boil-off shrinkage in the range 0% to 2%. Staple,-

fibers having physical properties outside the ranges enumerated are not generally commercially acceptable for textile uses.

The term initial imodulus is defined as the slope of. the first reasonably straight portion of a stress-strain curve of the filament obtained by plotting tension on a vertical axis versus elongation on a horizontal axis as the structure is being elongated at the rate of 10% per minute. In almost every instance, this first reasonably straight portion is also the steppest slope to be found on the curve. The values as used herein are in units of x grams per denier per percent elongation. V p Although the majority of references in the prior art giving polymer molecular weight in terms of solution viscosity have been in terms of intrinsic viscosity, the narrow range of viscosity covered by this invention requires more precise measurement than can be made with the usual intrinsic viscosity measurement. Consequently, the viscosity range has been defined in terms of relative viscosity at 10% concentration which affords the possibility of a considerably improved precision of measurement.

The reduced pilling tendency of the staple fibers of this invention is best observed in actual Wear tests of garments prepared from fabrics containing these fibers, but may also be demonstrated in a laboratory test such as that described by the American Society for Testing Materials in ASTM D'\l37555T, Test for Pilling Propensity of Textile Fabrics-Part CBrush and Sponge Method, or the Random Tumble P-illing Test" which is in the balloting process by A.S.T.M. for use as a standard testing procedure.

The experimental data plotted in the drawing were obtained by using fabric types chosen to emphasize the effects under examination and thereby clearly indicate the critical viscosity range of the invention. Subjective ratings of pilling were made upon fabrics of relatively loose construction which are recognized to have a greater pilling propensity than fabrics of tight construction. Ratings of frosting were made on deeply dyed fabrics of tight construction which show frosting much more readily than lighter colored fabrics or more loosely constructed fabrics. Obviously, by proper choice of certain fabric constructions, some acceptable fabrics may be prepared from staple fiber having a relative viscosity outside the scope of this invention. Conversely, staple fibers within the scope of this invention lend themselves to a much broader choice of fabric types than is possible with fibers outside the scope of the invention.

The performance of the fibers of this invention may be further improved on the one hand by reducing filament tenacity, which further reduces piliing in otherwise borderline fibers of the higher relative viscosities, within the area ABC of the drawing and on the other hand by more severe heat or steam relaxing treatment of the drawn filaments, which reduces frosting tendency and thereby allows borderline fibers having the lower viscosity polymer of the area ABC of the drawing to be used for longer periods of time before frosting becomes prohibirive.- As an example of the effect of higher heat relaxing temperature, raising the temperature in the heat relaxing step from to C. allows a reduction of about one unit in relative viscosity before equivalent frosting is. observed. The effect of reduced tenacity is as expected since it is obvious that weaker filaments will allow pills to be pulled off the fabric surface more easily. However, the use of lower tenacity filaments is not appealing since yarns formed from such filaments, being weaker, are more difficult to process without breakdown of threadlines.

The invention will be further illustrated but is not intended to be limited by the following examples.

EXAMPLE I Polyethylene terephthalate homopolyester having a relative viscosity of 16 is melt-spun and wound up at a speed of 1500 yards per minute to give a spun yarn with a filament denier of 9.0. The spun yarn is combined into a tow having a total denier of 90,000 and drawn in a water bath held at a temperature of 90 C., at a draw ratio of 3.16, crimped in a stufiing box crimper, and relaxed in air at a temperature of 140 C. The resulting yarn is found to have a filament denier of 3.04, a tenacity of 3.63 grams per denier, a break elongation after boil-off of 47%, and a boil-01f shrinkage of The relative viscosity of the polymer making up the fiber is 15.8. The fibers are cut into 2 /2 inch lengths and spun into yarn (sample Ia) of the well-known worsted system, A Worsted type fabric with a 2 X 2 twill construction is woven from the yarn using a 29/2 yarn in the warp and a 29/2 yarn in the filling. Both single yarns have a Z twist of 17 turns per inch and are plied with an S twist of 19 turns per inch. The fabric thus pre pared is given the usual finishing treatment consisting of scouring, dyeing in the presence of a carrier, heat setting on a tenter frame at 300 F. for one minute, brushing and shearing, followed by semi-decating.

The finished fabric is given the A.S.T.M. brush-andsponge pill count test and compared with a fabric made from polyethylene terephthalate fiber (sample Ib) having a relative viscosity of 27 but similar in every other way to the fiber described above. After 150 minutes of testing, the fabric prepared from the fiber of this invention has a pill count of less than 3 pills per square inch whereas the fabric prepared from fiber having a relative viscosity of 27 has a pill count of 22 per square inch.

The two fabrics mentioned above are made into trousers and worn for 300 hours. After this wearing, the trousers prepared from the fiber having a relative viscosity of 27 are found to be pilled to a very objectionable extent, giving a very unsightly appearance, Whereas the trousers prepared from fiber having a viscosity of 15.8 are quite acceptable, being pilled to only a minor extent. Similarly tested, trousers prepared from fiber having a relative viscosity of 18 and a break elongation of 45% (sample Ic) are found to be pilled to an objectionable extent.

The fabric prepared from fiber having a viscosity of 15.8 is compared with a fabric prepared from fiber having a relative viscosity of 12 and a break elongation of 43% (sample Id). After a 300-hour wear test, the trousers from the fiber having a relative viscosity of 12 Show a considerable amount of frosting at points such as the belt loops, seams, and edges of the pockets whereas the trousers prepared from polymer having a relative viscosity of 15.8 show no frosting at Wear points.

Similar comparison tests are made with a fabric made from fiber having a relative viscosity of 13.5 and a break elongation of 40% (sample 1e). In this case also the fabric having the relative viscosity of 13.5 exhibits excessive frosting after a wear test, whereas the fabric prepared from fiber having a relative viscosity of 15.8 does not exhibit excessive frosting.

A similar sample in which the fiber has a relative viscosity of .5 and a break elongation of 24% (sample 1 gives satisfactory pilling performance but is characterized by excessive frosting.

A sample in which thefiber has a relative viscosity of 16.6 and a break elongation of 23.5% (sample Ig) exhibits objectionable pilling performance and also is only- Table 1 Fiber Relative Break Pilling Frosting Sample Code Viscosity Elonga- Test 1 Test 1 tion, Percent 15 .8 47 A A 27 47 O A 18 45 O A 12 43 A O 13 .5 40 A O 15 .5 24 A O 16 .6 23 .5 O B 1 Test ratings: A =acceptable; B =borderline; O =objectionable;

EXAMPLE II A copolymer of polyethylene terephthalate containing 2 mol percent of the radical derived from sodium 3,5- di(carboxy)benzenesulfonate and having a relative viscosity of 17 is melt-spun and wound up at a speed of 1200 yards per minute to give an undrawn yarn having a filament denier of 9.5. The spun yarns are combined to give a tow having a total denier of 400,000 and drawn at a speed of 300 yards per minute in water at a temperature of C. using a draw ratio of 3.32. After crimping in a stufiing box crimper and relaxing in air at a temperature of C., the tow is found to be composed of filaments having a relative viscosity of 17, a denier of 3.04, a tenacity of 3.33 grams per denier, a break elongation after boil-off of 35%, an initial modulus of 50 grams per denier, and a boil-off shrinkage of substantially 0%. Thetow is cut into a 2 /2 inch staple fiber and spun into yarn (sample I la) of 29/2 cotton count with 19 turns per inch 8 in the singles and 17 turns per inch 2 in the ply. The yarn is woven into a 2 x 2 twill worsted type fabric, and finished as described in Example I.

The fabric is tested for pilling propensity using the A.S.T.M. brush-and-sponge pilling test. It was found after 240 minutes to have a pill count of less than 5 pills per square inch. A similar fabric prepared from fiber having a polymer viscosity of '23 and a break elongation of 36% (sample 11b) is found to have a pill count greater than 30 pills per square inch in the same test.

Trousers made from the fabric of this example are wear tested for 300 hours and found to be quite acceptable both in subjective rating of pilling performance and frosting performance. Similar trousers prepared from fiber having a polymer relative viscosity of 14.5 and a break elongation of 35% show signs of objectionable frosting at wear points on the same wear test, and fibers with a relative viscosity of 12 (sample Ild) result in an even greater degree of frosting in this test.

When the fabric of this example (sample Ila) is compared with a similar fabric composed of fibers having a relative viscosity of 19 (sample He) in a 300-h0ur wear test, the. 19 viscosity fabric exhibits objectionable pilling in contrast to the fabric of this example although not as severe as that exhibited by a fabric composed of filaments having the more normal viscosity of 23.

The fabric of this example (sample Ila) is found to be equivalent to a fabric having a relative viscosity of 23 in wrinkle resistance and crease recovery as judged subjectively in wear tests.

The test results of the samples described in this example are summarized in the following table.

1 Test ratings: A=acceptable; O=objectionabla EXAMPLE III A copolymer of polyethylene terephthalate containing in the polymer chain 2 mol percent of the radical derived from sodium 3,5-di(carboxy)benZenesul-fonate and having a relative viscosity of 15.2 is melt-spun and wound up at a speed of 1200 yards per minute to give an undrawn yarn having a filament denier of 9.6. The spun yarns are combined to give a tow having a total denier of 80,000 and drawn at a speed of 375 yards per minute in water at a temperature of 90 C., using a draw ratioof 3.16. After crimping in a stuifing box crirnper and relaxing in air at a temperature of 140 C. the tow is found to be composed of filaments having a relative viscosity of 15.2, a denier of 3.06, a tenacity of 3313 grams per denier, a break elongation of 43%, an initial modulus of 3 3 grams per denier, and a boil-off shrinkage of substantially The tow is cut into a 2% inch staple fiber and spun into a yarn of 33/2 cotton count with 18 turns per inch Z in the singles and 23 turns per inch 8 in the ply. The yarn (sample Illa) is woven into a 1 x lplain weave worsted type fabric. The fabric thus prepared is given the usual finishing treatment consisting of scouring, dyeing in the presence of a carrier, heat setting on a tenter frame at 350 F. for one minute, brushing and shearing, semidecating, followed by rotary pressing.

The finished fabric is given a random tumble pill test and compared with a fabric made from a similar copolymer of polyethylene terephthalate having a relative viscosity of 15.5 with a tenacity of 4.09 grams per denier; a break elongation of 28%, an initial modulus of 45 grams per denier, and a boil-off shrinkage of approximately 0% (sample 1111b). In all other respects the fabrics are similar. After 120 minutes of pill testing (comparable to 600 hours wear) both fabrics exhibited no pills. A similar fabric of polyethylene terephthalate copolymer having a relative viscosity of 27 (sample IIIc) pilled excessively after just 30 minutes testing (comparable to 150 hours wear).

The two fabrics described above (Ha and Illb) were made into trousers and worn for 600 hours. After this wearing, the trousers prepared from the fiber having a relative viscosity of 15.5 and an elongation of 28% were i found to have frosted objec-tionably at points such as belt loops, seat seams, and pocket edges, whereas those trousers of the fiber having a relative viscosity of 15.2 and an elongation of 43% were only slightly frosted and still considered acceptable.

Similar comparison tests were made with fabrics of the same polyethylene terephthalate copolymer at relative viscosities of 16.8 (HId), 18.0 (=H1e), and 20.0 (111)), all samples having tenacities in the range of 3.40 to 3.88 grams per denier, and elongations ranging from to 41%. None of these items exhibited objectionable frosting after 600 hours wear in trousers. The higher viscosity items (111a and iIIIf) were found to pill in the random tumble pill test to an objectionable level after 30 minutes testing whereas the 16.8 relative viscosity sample (I IId), although slightly pilled, was still considered acceptable after 60 minutes of testing.

The test results of the samples described in this example are summarized in the following table.

Table 3 Fiber Relative Break Pllling Frosting Sample Code Viscosity Elonga- Test 1 Test 1 tion, Yercent 15 .2 43 A A 15.5 28 A O 1 Test ratings: A=acceptable; O=objectionable.

EXAMPLE IV A copolymer of polyethylene terephthalate is prepared containing in the polymer chain 3.5 mol percent of 1 the radical derived from sodium 3,5-di(carboxy)benzenesulfonate. The polymer is finished in thre portions having viscosities of 14.8, 17.0, and 18,8, respectively. These polymers are spun into fibers and drawn, using a draw ratio of 3.06. Fabrics are prepared from them as described in Example 111. Pilling and frosting tests are ca'rried out with the results shown in the following table.

Table 4 Fiber Relative Break Filling Frosting Sample Code Viscosity Elonge- Test Test 1 tlon, Percent 14.8 42 A o 17 39 A A 18.8 44 O A 'lest ratings: A=acceptable; O =objectionable EXAMPLE V Copolymers of polyethylene terephthalate containing in the polymer chain 3 mol percent of the radical derived from sebacic acid are prepared having relative viscosities of 14.5, 16.5, and 18.5, respectively. The polymers are spun into fiber and drawn, using a draw ratio of 3.30.

The fiber is Woven into fabric following the general procedure of Example Ill. The results of pilling and frosting tests on these three items are summarized in the following table.

Table 5 Fiber Relative Break Pilllng Frosting Sample Code Viscosity Elimga- Test 1 Test t on, Percent 14.5 45 a Y 0 1G .5 42 A A 18.5 40 O A 1 Test ratings: A=acceptable; O=objectlonable.

, EXAMPLE VI 'A polyethylene oxide glycol having an average molecular weight of 1000 (Carbowax 1000) is incorporated in polyethylene terephthalate to give a copolymer containing 2 mole percent of the polyethylene oxide glycol unit. The polymer which has a relative viscosity of 16 is spun into fiber which when drawn using a draw ratio of 3.20 has a tenacity of 3.5 grams per denier and a break elongation after boil-01f of 43%. Fabric samples are prepared from this fiber following the general procedure of Example I and tested for resistance to pilling and frosting. The fabric samples are rated acceptable in both the pilling and frosting tests.

EXAMPLE VI I Three copolymer batches of polyethylene terephthalate are prepared, each containing 4 mol percent oftetramethylene glycol. The polymers are spun into yarn, drawn using a draw ratio of 3.35, and converted to staple fiber according to known procedures. Fabric samples are prepared therefrom. The fabric samples are tested for pilling land frosting performance with the results shown in the following table.

Table 6 Fiber Relative Break Pilling Frosting Sample Code Viscosity Elpnga- Test 1 Test 1 t on Perceiit 15 38 A O 17 41 A A 19 43 O A 1 Test ratings: A=acceptable; O=objectionable.

EXAMPLE ViII Several samples of the homopolyester, polyethylene terephthalate, are processed according to the procedure of Example I to give fabric samples in which the fiber viscosity and tensile properties cover a range of values. The fabric samples are tested for pilling and frosting as previously described with the results shown in the following table.

Table 7 Fiber Relative Break Pilling Frosting Sample Code Viscosity Elonga- Test 1 Test 1 tion, Percent 14 .7 29 .5 A O 14.7 36 A B 13 .5 47 A B-O 15 .1 46 A A 14 .6 47 A A 13 .2 50 A O 1 Test ratings: A=acceptable; B=borderline; O=objectinable.

EXAMPLE IX Several samples of the copolyester of polyethylene terephthalate containing 2 mol percent of the radical derived from sodium -3,5-di(carboxy)benzenesulfonate are processed into fabric according to the procedure of Example II. The fabric samples produced contain fibers covering a range of viscosities and tensile properties. The fabric samples are tested for resistance to pill-in-g and frosting with the results summarized in the following table.

1 Test ratings: A= acceptable; 13 =borderline; O =objectionable.

EXAMPLE X A random copolyester of polyethylene terephthalate and polyethylene isophthalate, in which mol percent of the acid linking units are isophthalate units and 95% of the acid linking units are terephthalate units, is meltspun and wound up at a speed of 1260 yards per minute to give a spun yarn having a filament denier of 11.8. The spun yarn is combined into a tow having a total denier of 85,000 and drawn in a water bath held at a temperature of C. at a draw ratio of 3.46, criinped in 2. stuffing box crimper, and relaxed in air at a temperature of C. The resulting yarn is found to have a filament denier of 3.0, a tenacity of about 3 grams per denier, and a break elongation after boil-off of about 35%. The relative viscosity of the polymer making up the fiber is 18.5. The fibers are cut into 2 /2 inch lengths and spun into yarn of the well-known worsted system. A worsted type fabric with a 2 x 2 twill construction is woven from the yarn using a 29/2 yarn in the warp and a 29/2 yarn in the filling. Both single yarns have a Z twist of 17 turns .per inch and are plied with an S twist of 19 turns per inch. The fabric thus prepared is given the usual finishing treatment consisting of scouring, dyeing in the presence of a carrier, heat setting on :a tenter frame at 300 'F. for one minute, brushing and shearing, Semideca-ting, followed by rotary pressing.

The finished fabric is given a random tumble pill test as in Example III and found to have a rating between borderline and acceptable. When the fabric is made into trousers and subjected to a wear test to determine resist ance to frosting, the fabric is found to have a frosting rating of acceptable.

The foregoing examples illustrate the practice of this invention but, as previously stated, are not intended to be limitative since polyethylene terephthalate copolymers containing residues of various acids and glycols and having relative viscosities as heretofore described may be substituted directly for those used in the examples.

The fibers of the present invention are useful not only in fabrics woven entirely from the fibers described but also in fabrics which include blends of other synthetic as Well as natural fibers. Particularly desirable dare blends of rayon and Wool in which the high tenacity, highly pilland frost-resistant fibers of this invention are included.

This application is a continuation-in-part of our copending application Serial No. 707,826, filed January 8, 1958, and now abandoned.

As many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not to be limited to the specific embodiments thereo except as defined in the appended claims.

We claim:

1. As an article of manufacture, a drawn textile fiber in staple form having a high resistance to pilling and frosting when incorporated in a textile fabric, said fiber having a tenacity in the range from about 2.8 to about 4.2 grams per denier and a break elongation from about 26% to about 55%, said fiber being comprised of ester linking units of a synthetic fiber-forming linear condensation polyester of ethylene glycol and terephthalic acid and up to 8 mol percent of other ester linking units having intralinear carbon and oxygen atoms, at least 92 mol percent of said polyester consisting of intralinear structural units having the formula said polyester having a relative viscosity in the range from about l3.5+0.5x to about 16.5+O.5x Where x is equal to the mol percent of said other ester linking units,

said relative viscosity being determined in a 10% solution of said polyester in a mixture of 10 parts of phenol and 7 parts of 2,4,6-trichlorophenol at 25 C., said break elongation and said relative viscosity having the relation ship defined by the area ABC on the graph in the drawing.

2. The fiber of claim 1 wherein said relative viscosity is in the range from about 14.5+0.5x to about 15.-5+0'.5x and said break elongation has the relationship to said relative viscosity as further defined by the area DEF on the graph in the drawing.

3. The fiber of claim 1 wherein said other ester linking units bear at least one sulfonate group in the form of a metallic salt.

4. The fiber of claim 3 wherein said other ester linking units are 3,5-di(carboxy)benzene sulfonate units and are present in an amount up to about 3.5 mol percent.

5. A textile yarn having a high resistance to pilling and frosting comprised of staple fibers having a tenacity in the range from about 2.8 toj about 4.2 grams per denier and a break elongation from about 26% to about 55%, said fiber being comprised of ester linking units of a synthetic fiber-forming linear condensation polyester of ethylene glycol and terephthalic acid and up to 8 mol percent of other ester linking units having intralinear carbon and oxygen atoms, at least 92 mol percent of said polyester consisting intralinear structural units having the formula said polyester having a relative viscosity in the range from about 13.5+0.5x to about l6.5+0.5x where x is equal to the mol percent of said other ester linking units, said relative viscosity being determined in a 10% solution of said polyester in a mixture of 10 parts of phenol and 7 pants of 2,4,6-trichlorophenol at 25 'C., said break elongation and said relative viscosity having the relationship refined by the area ABC on the graph in the drawing.

6. The textile yarn of claim wherein said relative viscosity is in the range from about l4.5+0.5x to about 15.5+0.5x and said break elongation has the relationship to said relative viscosity as further defined by the area DEF on the graph in the drawing.

7. The textile yarn of claim 5 wherein said other ester linking units bear at least one sulfonate group in the form of a metallic salt.

about 4.2 grams per denier and a break elongation from 8. The textile yarn of claim 7 wherein said other ester linking units are 3,5-di(carboxy)benzene sulfonate units and are present in an amount up to about 3.5 'mol percent.

9. A textile fabric having a high resistance to pilling and frosting prepared from yarn comprised of staple fiber having a tenacity in the range from about 2.8 to

about 26% to about said fiber being comprised of ester linking units of a synthetic fiber-forming linear condensation polyester of ethylene glycol and terephthalic acid and up to 8 mol percent of other ester linking units having intralinear carbon and oxygen atoms, at least 92 mol percent of said polyester consisting of intralinear structural units having the formula said polyester having a relative viscosity in the range.

from about l3.5+0.5x to about l6.5+0.5x where x is equal to the mol percent of said other ester linking units, said relative viscosity being determined in a 10% solution of said polyester in a mixture of 10 par-ts of phenol said break elongation and said relative viscosity having the relationship defined by the area ABC on the graph in the drawing.

and 7 parts of 2,4,6-trichloropheno1 at 25 C.,-

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,104,450 September 24, 1963 John M, Christens et a1.

It is hereby certified that error appears in the above numbered petent requiring correction and that the said Letters Patent should read as corrected below Column 4, line 21, for "steppest" read steepest column 8, line 19, for "thre" read three line 20, for "18,8" read 18.8 column 11, line 30, for "refined" read defined Signed and sealed this 7th day of April 1964.

(SEAL) An t; EDWARD J. BRENNER ERNEST W. SWIDER Attesting Officer Commissioner of Patents 

1. AS AN ARTICLE OF MANUFACTURE, A DRAWN TEXTILE FIBER IN STAPLE FORM HAVING A HIGH RESISTANCE TO PILLING AND FROSTING WHEN INCORPORATED IN A TEXTILE FABRIC; SAID FIBER HAVING A TENACITY IN THE RANGE FROM ABOUT 2.8 TO ABOUT 4.2 GRAMS PER DENIER AND A BREAK ELONGATION FROM ABOUT 26% TO ABOUT 55%, SAID FIBER BEING COMPRISED OF ESTER LINKING UNITS OF A SYNTHETIC FIBER-FORMING LINEAR CONDENSATION POLYESTER OF ETHYLENE GLYCOL AND TEREPTHALIC ACID AND UP TO 8 MOL PERCENT OF OTHER ESTER LINKING UNITS HAVING INTRALINEAR CARBON AND OXYGEN ATOMS, AT LEAST 92 MOL PERCENT OF SAID POLYESTER CONSISTING OF INTRALINEAR STRUCTURAL UNITS HAVING THE FORMULA -CO-(1,4-PHENYLENE)-COO-CH2-CH2-OSAID POLYESTER HAVING A RELATIVE VISCOSITY IN THE RANGE FROM ABOUT 13.5+0.5X TO ABOUT 16.5X WHERE X IS 